The uptake of tritiated methotrexate (MTX-3H) was studied in a s.c.-implanted mouse ependymoblastoma and normal mouse brain after a single i.v. injection. An autoradiographic technique suitable for diffusible tracers was used, and autoradiographs of tumor and brain were prepared 2, 10, and 60 min after injection.

At 2 min, the tumors showed a large amount of MTX-3H in the interstitial space and much less in tumor cells. At 10 min, the high interstitial uptake persisted, but in addition most neoplastic cells had become labeled. The tumor showed very little remaining interstitial radioactivity but very high cellular uptake 60 min after injection. In the brain at all times after injection, there was very little extravascular uptake.

These studies show that this glial tumor rapidly accumulated MTX-3H from the bloodstream. Initially, interstitial uptake was high, but cellular uptake was delayed. However, once cellular uptake occurred, it persisted for at least 60 min.

Further studies are needed for determination of how long MTX-3H remains in the neoplastic cells and for comparison of uptake in intracerebral and s.c. implants of the ependymoblastoma.

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This investigation was supported by Ontario Cancer Treatment and Research Foundation Grant 247.

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